To enhance bass response, some loudspeaker systems may include a passive radiator or a bass reflex port, in addition to a speaker. A passive radiator is similar to a speaker, but lacks a voice coil and magnet. In a passive radiator, the mass of the cone, the radiation inertia, and the stiffness of the suspension system form a resonant system which interacts with the speaker by coupling through the enclosed air of the speaker housing. A bass reflex port is an open tube that couples the interior of a speaker housing to air outside the speaker housing.